Contemporary automatic dishwashers for use in a typical household include a tub and an upper and lower rack or basket for supporting soiled utensils within the tub. A spray system and a filter system are provided for re-circulating wash liquid throughout the tub to remove soils from the dishes. Some conventional dishwashers have a turbidity sensor to measure turbidity of a wash liquid. The turbidity can be viewed as a measurement of the “dirtiness” of the wash liquid, due to the presence of suspended particulate matter. The turbidity level indicates the amount of food soil that has been removed from the dishes and enables the dishwasher to determine if the re-circulating wash liquid is appropriate.
These types of sensors are affected by conditions such as buildup on the optical surfaces, light source output drift, and photodiode sensitivity drift. Compensation techniques can be used to lessen the effect of buildup on the optical surfaces, so that the turbidity measuring can be continued even if there is buildup on the optical surfaces of the turbidity sensor. There is a limit to these compensation techniques, as the turbidity sensor can get too dirty to generate reliable data. In this case, the sensor is turned off and the dishwasher switches to a default setting that does not use the turbidity measurements.